Cerium promoted Fischer-Tropsch catalysts

ABSTRACT

New Fischer-Tropsch catalysts containing a Lanthanide Group element, such as cerium, exhibit improved activity over conventional catalysts and exhibit a reversal in the olefin/paraffin ratio of low molecular weight hydrocarbons. The catalyst comprises: 
     (a) a Group VIII metal oxide; 
     (b) a Group IIB metal oxide; 
     (c) a Group IVB and/or VIIB metal oxide; 
     (d) a Group IA metal oxide; and, 
     (e) a Lanthanide group metal oxide.

BACKGROUND OF THE INVENTION

This invention relates to improved Fischer-Tropsch catalysts containingcerium and their use in CO/H₂ hydrocarbon synthesis in which thecatalysts display enhanced reactivity and a reversal of olefin/paraffinselectivity versus traditional non-cerium containing F-T catalysts.

The search for processes to provide alternate feedstocks, for chemicals,and particularly low molecular weight olefins, has been prompted by thegrowing shortage of traditional petroleum reserves, as well as theincreasing instability of international hydrocarbon sources.

One approach to the problem has been the utilization of theFischer-Tropsch synthesis in producing a selective product distributionof olefinic hydrocarbons also containing paraffins, in varyingolefin/paraffin ratios, depending on the catalyst composition andreaction conditions. Various catalyst combinations of elements have beentested in the past, of which the chief constituent element has beennickel, cobalt, iron or ruthenium. Secondary products in the processesinclude branched chain hydrocarbons, aliphatic alcohols, aldehydes andacids.

Ruhrchemie Aktiengesellschaft has disclosed in GB Pat. No. 1,512,743, GBPat. No. 1,553,361, 1,553,362 and 1,553,363, catalysts pertaining to theselective production of C₂ -C₄ olefins from synthesis gas (preferablycarbon monoxide and hydrogen). The inventions embody a process for theproduction of one or more unsaturated hydrocarbons comprising catalytichydrogenation of a carbon oxide with hydrogen at 250° C. to below 350°C. and a total pressure of 10 to 30 bars in the presence of a catalystwhich contains (a) one or more oxides selected from difficult-to-reduceoxides of metals from Group IVB or a lower oxide of Group V and/or GroupVII of the Periodic Table; and (b) one or more metals selected fromGroup VIII of the Periodic Table, the ratio by weight of the metal ormetals of the one or more oxides (a) to the one or more metals (b) beingin the range 1:2 to 1:10. Additionally, the catalysts can contain GroupIA alkali metal and Zn salt promoter agents. In the process, good yieldsof unsaturated hydrocarbons, especially gaseous olefins, are reported.

U.K. Pat. No. 833,976 discloses a catalyst for the production ofethylene from CO and hydrogen consisting of four components: the first agroup including zinc oxides; the second group preferably being cobalt,although iron also could be used, with the proviso that the Group VIIImetal component constitutes not more than 10% of the total weight of thecatalyst, and being activated by compounds which may include manganeseoxide; the third group including an oxide of titanium and/or the rareearth elements; and the fourth group being a carbonate, oxide orhydroxide of an alkali metal. The reaction preferably is conducted at atemperature of from 350° C. to 520° C., preferably from 350° C. to 450°C.

U.K. Pat. No. 506,064 discloses the preparation of an iron-containingFischer-Tropsch catalyst. The catalyst also may contain minor amounts ofalkali compounds which are practically undecomposed up to 1,000° C. Thispatent also discloses a lengthy list of other compounds that may beadded, including titanium, manganese and cerium oxides or hydroxides.

U.S. Pat. No. 4,199,523 discloses a Fischer-Tropsch catalyst containingat least 60% iron. In addition, promoters such as copper and/or silverand alkali are desirable. Other additives, such as alkaline earth metalcompounds, zinc oxide, manganese oxide, cerium oxide, vanadium oxide,chromium oxide, and the like may also be used.

U.S. Pat. No. 4,291,126 discloses a catalytic process for themanufacture of linear saturated alcohols from CO and H₂. The catalystcomprises copper; cobalt; a third metal selected from chromium, iron,vanadium and manganese; a fourth metal which is a rare earth metal; anda fifth metal which is an alkali metal.

U.S. Pat. No. 4,211,673 discloses a catalyst composed of a rare earthmetal, such as cerium, and a transition metal, such as iron, for thereduction of CO to produce oxygenated hydrocarbons.

U.S. Pat. No. 4,186,112 also discloses a Fischer-Tropsch catalyst whichmay include cerium.

Other patents which disclose the use of cerium include U.S. Pat. Nos.4,162,234; 4,001,317; 3,992,238; 3,932,551; and 3,615,807.

It is desirable to provide a catalyst and/or process for significantlyincreasing the activity of a low molecular weight olefin producingcatalyst while concurrently maintaining a high olefins product slateunder standard olefin producing conditions.

SUMMARY OF THE INVENTION

It has been discovered that a sintered, iron-containing spinelcombination metal oxide catalyst containing cerium as a componentenhances the catalyst activity and maintains a high olefins/paraffinsproduct distribution during a Fischer-Tropsch alpha olefin synthesis.

It has also been discovered that, under selected conditions oftemperature and pressure in conjunction with the catalyst describedabove, one can also obtain unsaturated hydrocarbons of low molecularweight in good yield. Alternatively, higher molecular weight species maybe obtained under suitable conditions.

The catalyst may be prepared by contacting a composition comprising anelement or elements from Group VIII, IVB, and/or VIIB, IIB, IA and anelement or elements from the lanthanide series. The preparation of thecatalyst employed in the process of the invention may be initiated froma variety of precursors. The manner and means of integrating theseprecursors to a final state of the catalyst may be accomplishedutilizing standard practice techniques such as blending,co-precipitating, impregnation, fusion and the like. The followingdisclosure will illustrate to one skilled in the art several preferredexamples of catalyst composition preparation, reactivity, selectivityand activity.

The catalyst comprises about 65 to about 95 weight percent of Group VIIImetal oxides such as the oxides of Fe; a Group IVB metal oxide such asTiO₂, and/or a Group VIIB metal oxide, such as MnO, ranging from about10 to about 30 weight percent; a Group IIB metal oxide, such as ZnO,ranging from about 5 to about 20 weight percent; a Group IA metal oxide,such as the oxides of cesium, rubidium, potassium and mixtures thereofranging from about 1 to about 10 weight percent; and a Lanthanide groupmetal oxide, such as CeO₂, ranging from about 1 to about 10 weightpercent.

By this invention, there is provided, a hydrocarbon synthesis catalystcomposition comprising a sintered combination of metal oxides having thefollowing components in stated weight percentage of the catalystcomposition:

(a) about 5-80 weight percent Fe oxide;

(b) about 4-20 weight percent Zn oxide;

(c) about 10-40 weight percent Ti and/or Mn oxide;

(d) about 1-5 weight percent K, Rb, or Cs oxide or mixtures thereof; and

(e) about 1-10 weight percent Ce oxide.

Where the catalyst contains iron, the catalyst preferably exhibits theX-ray diffraction pattern of an iron-containing spinel or mixturethereof and a Lanthanum group metal oxide, such as cerium oxide. Thespinel may comprise magnetite, Fe_(3-x) Mn_(x) O₄, Fe_(3-x) Zn_(x) O₄,Fe_(3-x) Ti_(x) O₄ or mixtures thereof where x ranges between about 0.15and about 2.4. The cerium oxide preferably is a homogeneouslydistributed component, the concentration of the Group IA metal oxide isless than about 2 weight percent of the catalyst composition and thecerium oxide concentration ranges from about 2 to about 5 weight percentof the catalyst composition.

In a preferred embodiment the metal atoms are present in the followinggeneralized and more preferred ratios.

    ______________________________________                                                     Generalized                                                                            More Preferred                                          ______________________________________                                        Fe             0.8-1.2    1.0                                                 Zn             0.05-0.08  0.065                                               Ti and/or Mn   0.25-0.35  0.30                                                Ce             0.010-0.15 0.030                                               K, Rb and/or Cs                                                                              0.010-0.15 0.030                                               ______________________________________                                    

This catalyst composition may be supported on an inert support, such asalumina, silica or magnesia. Further provided is a process for preparinga catalyst composition comprising the steps of:

(a) slurrying an aqueous suspension of oxides of: iron, zinc; titaniumand/or manganese; the carbonates of potassium, rubidium, and/or cesiumand cerium carbonate;

(b) heating the aqueous slurry to a temperature of at least about 90° C.and;

(c) sintering the resulting solid in an oxygen-containing atmosphere, ata temperature in the range of about 400° C. to about 1200° C. until theX-ray diffraction pattern of the solid is substantially that of at leastone iron-containing spinel in the form of Fe_(3-x) M_(x) O₄ where M=Zn,and/or Mn and/or Ti, and x ranges between about 0.15 and about 2.4, inan oxide matrix comprising CeO₂.

In a preferred embodiment, the resulting solid is sintered at atemperature of about 100° C. to about 1200° C. for a period of timeranging between about 16 to about 24 hours.

Still further provided is a hydrocarbon synthesis process comprising thesteps of:

(a) contacting a feedstream of CO and H₂ in a molar ratio in the rangefrom 0.5 to 4.0:1, preferably 0.66 to 2.0:1, more preferably betweenabout 1.0:1.0 and about 2.0:1 with the previously described catalyst ata temperature in the range of about 200° to 350° C., a pressure in therange of about 1 to 50 atmospheres (0.1 to 5 MPaA) preferably betweenabout 5 and about 25 atmospheres and a space velocity in the range ofabout 10 to 10,000 v/v/hr. preferably between about 500 and about 1500v/v/hr., thereby producing a hydrocarbon product mixture containingethylene and ethane, in which the ethylene/ethane molar ratio is greaterthan one; and,

(b) recovering the hydrocarbon product.

DETAILED DESCRIPTION OF THE INVENTION I. Catalyst Composition

The catalysts of the present invention comprise a sintered combinationof metal oxides whose composition, expressed as weight percentage of thecatalyst composition for the individual metal oxides is: about 5-80weight percent Fe oxide as Fe₂ O₃ ; about 4-20 weight percent Zn oxideas ZnO; about 10-40 weight percent Ti and/or Mn oxide as TiO₂ and/orMnO₂ ; about 1-5 weight percent K,Rb and/or Cs oxide as K₂ O, Rb₂ Oand/or Cs₂ O; and about 1-10 weight percent Ce oxide as CeO₂. Thecatalyst, after sintering, contains a series of Fe-Zn and Fe-Ti and/orMn spinels dispersed in an evenly distributed CeO₂ matrix.

The Group VIII precursors, preferably Fe containing precursors useful inproviding the catalysts of the instant invention include Fe₂ O₃, Fe₃ O₄,as well as salts, such as the hydroxide, nitrate, chloride, carbonate,which can be converted to oxides in the high temperature sintering step.A preferred precursor is Fe₂ O₃. The quantity of the precursor used isadjusted to achieve the desired final composition, after sintering,wherein Fe as the oxide is present at 5-80%, preferably greater than50%, of the total weight of the final composition.

The Group IIB component, preferably the Zn component of the instantcatalyst, can be derived from the oxide, ZnO, or salts, such as thehydroxide, nitrate, chloride or carbonate, which can be converted to theoxide in the high temperature sintering step. The preferred Zn precursoris ZnO. The level of precursor employed is adjusted so the finalcomposition will contain about 4-20 weight percent Zn as the oxide. Znpresent in the final composition may be present in that form or in solidsolution with Fe oxide as a spinel.

The Group IV component such as Ti and/or the Group VIIB component, suchas the Mn component of the instant catalyst, is charged as the oxide,preferably TiO₂ or MnO₂. These materials are charged at levels such thatthe final composition will contain them as oxides at 10-40 weightpercent levels, although they may be present in the form of solidsolutions with the iron-containing component.

The alkali metal Group IA component, preferably K, Rb, Cs or mixturesthereof, is charged as salt, e.g., carbonate, bicarbonate, hydroxide,nitrate, or other salts, which can be converted to oxides, K₂ O, Rb₂ O,Cs₂ O, or mixtures thereof, in the sintering step. These materials arecharged such that the final composition will contain about 1-5 weightpercent alkali expressed as the oxide, preferably less than 2 weightpercent of the final catalyst composition.

The Lanthanum group component, preferably a Ce component of the instantinvention, is charged as the oxide or carbonate. These are charged inamounts such that the final composition contains about 1-5 weightpercent cerium as the oxide, CeO₂, preferably from about 2 to about 5weight percent of the final catalyst composition.

The catalyst precursor mixture is sintered in air at 800° C.-1,200° C.X-ray diffraction indicates that Fe₃ O₄ and a series of iron containingspinels are formed, i.e., Fe_(3-x) M_(x) O₄, where M is Zn, and Tiand/or Mn, and that these components are present in a CeO₂ matrix wherex ranges between about 0.15 and about 2.4.

Examples of catalyst compositions considered useful in the conversion ofCO/H₂ to α-olefins include oxide mixtures of Fe/Ti/Zn/Ce/K andFe/Mn/Zn/Ce/K wherein the metal atom ratios Fe:Ti and/or Mn:Zn:Ce:K are0.8 to 1.2:0.25 to 0.35:0.05-0.08:0.010-0.15:0.010-0.15 and, preferablyabout, 1.0:0.30:0.065:0.030:0.030, respectively.

The Ce/K metal atom ratio can be varied from about 3/1 to 1/3 while apreferred ratio is about 1/1.

The sintered mixed metal oxide catalysts of this invention are red-brownor red-purple in color, have BET surface areas ≦2 m² g, and are highlycrystalline in nature as shown by x-ray diffraction. Powder diffractionanalysis shows the catalyst to comprise a complex mixture of phasesincluding hematite, magnetite, ilmenite (when TiO₂ is present) and aseries of mixed spinels Fe_(3-x) M_(x) O₄ wherein M is Zn and Ti and/orMn and x ranges between about 0.15 and about 2.4, all in the presence ofa discernible CeO₂ phase. The combined chemical and physical propertiesof these catalysts are thought to influence its behavior under COhydrogenation reaction conditions.

II. Method of Preparation of Composition

The catalysts of this invention are prepared from an aqueous slurry ofthe precursors, i.e., Fe/Ti or Mn/Zn/Ce/K oxides or salts, which is thenplaced under vacuum, e.g., 10 mm Hg, at 100° C. to remove excess water.The homogeneous mixture of solids is then sintered in air at atemperature of about 400° C. to about 1,200° C. until X-ray powderdiffraction indicates that a stable system has been obtained. Thepreferred sintering temperature is from about 1,000 to about 1,200° C.and the preferred sintering time is from about 16 to about 24 hours.

III. Olefin Synthesis Process

Prior to their use, catalysts are pretreated with 90% H₂ 10% N₂ at250°-600° C., preferably 450°-500° C., at 0.1 to 4 MPaA, preferably 0.5to 2 MPaA, at flow rates of 10-3,000 v/v catalyst/hr, preferably100-1,000 v/v catalyst/hr for 1-24 hours, preferably 5-10 hours.

In an olefin synthesis run using the preferred catalyst the temperaturemay be maintained within the range of about 200° C. to about 350° C.,preferably within the range of about 250° C. to about 300° C. Thepressure may be maintained within the range of about 0.1 to about 4 MPaA(about 1 to about 40 atmospheres), preferably within the range of about0.5 to 2.5 MPaA (about 5 to about 25 atmospheres). The space velocitymay be maintained within the range of about 10 to about 10,000 volumesof feed per volume of catalyst per hour (v/v/hr), preferably within therange of about 500 to about 1,500 v/v/hr. A fixed bed is preferred,although a fluidized bed and/or a slurry also may be used, sincebackmixing can be minimized to reduce the residence time and increaseselectivity of the primary reaction products. Although upflow of thefeed through the bed may function, downflow is preferred since it allowsfor more efficient removal of liquid products. The CO:H₂ molar ratio maybe maintained between about 0.5:1 and about 4.0:1, with a molar ratio ofabout 1.0:1.0 and about 2.0:1.0 being preferred. The resulting productsprimarily comprise C₂ to C₁₅ compounds in which the olefins compriseapproximately 40-70% by weight of the total products. The ethylene toethane molar ratio preferably will be greater than one.

EXAMPLE 1 Catalyst Preparation

The following metal oxides were mixed in a blender: iron oxide as Fe₂O₃, TiO₂, ZnO, and CeO₂ in the following proportions by weight:1.00:0.30:0.065:0.030 taken as gram-atoms of free metal. Afterthoroughly mixing, the mixture was sintered by heating at a temperatureof about 1050° C. in air for 24 hours, followed by reduction in a H₂atmosphere at about 500° C. for 7 hours.

Hydrocarbon Synthesis Runs

About 5 to 10 grams of the above-prepared catalyst were placed into astainless steel fixed bed downflow reactor. The catalyst was pretreatedby heating at a temperature of 500° C. in a 9:1 H₂ /N₂ atmosphere at apressure of 100 psia and space velocity of 100 v/v/hr., for 5 to 6hours. X-ray diffraction analysis showed that not all of the metaloxides were completely reduced. After pretreatment, the catalyst wascontacted with a 3:1 H₂ /CO molar ratio gaseous feedstream at a spacevelocity of 1737 v/v/hr., a pressure of 394 psia and a temperature of270° C. for 2-10 hours.

A comparison run was made under substantially the same conditions usinga catalyst prepared in accordance with the Example of G.B. Pat. No.1,512,743, the disclosure of what is incorporated herein by reference,having an average particle size of 1/32", an average surface area of 3m² /g, and having the composition Fe₂ O₃ :TiO₂ :ZnO:K₂ O, in a weightratio of about 1.0:0.3:0.065:0.03, taken as gram-atom ratios of the freemetals.

The results for the percent CO conversion as a function of time is givenfor both catalysts in the following Table I.

                  TABLE I                                                         ______________________________________                                        Time On Stream % CO Conversion                                                Minutes        Fe/Zn/Ti/Ce                                                                              Fe/Zn/Ti/K                                          ______________________________________                                        125            48         --                                                  135            --         17                                                  210            49         --                                                  215            --         8                                                   290            54         --                                                  300            --         7                                                   370            58         --                                                  375            --         6                                                   450            62         --                                                  455            --         7                                                   ______________________________________                                    

As is seen, the cerium-promoted catalyst exhibits an activity differenceof about 4- to 5-fold greater than the potassium-promoted catalyst andmaintains its catalytic activity over a longer period of time.

The following data in Table II illustrates the product distribution databy carbon number and aliphatic carbon type from both runs. Values listedas "1", are between 0 to about 1 percent as measured.

                  TABLE II                                                        ______________________________________                                                  Wt. Percent                                                         Carbon No.  Fe/Ti/Zn/Ce.sup.(a)                                                                       Fe/Ti/Zn/K.sup.(b)                                    ______________________________________                                        C.sub.1     35          33                                                    C.sub.2     27          14                                                    .sup. C.sub.2.sup.=                                                                       1           25                                                    C.sub.3     1           1                                                     .sup. C.sub.3.sup.=                                                                       14          1                                                     C.sub.4     5           8                                                     .sup. C.sub.4.sup.=                                                                       8           1                                                     C.sub.5     1           1                                                     .sup. C.sub.5.sup.=                                                                       5           11                                                    C.sub.6     1           1                                                     .sup. C.sub.6.sup.=                                                                       9           12                                                    ______________________________________                                         .sup.(a) Data taken after 134 minutes onstream.                               .sup.(b) Data taken after 127 minutes onstream.                          

As is seen, olefin/paraffin ratios are substantially higher on the Kcontaining catalyst relative to the Ce containing analog.

EXAMPLE 2

Utilizing the catalysts, procedure and apparatus described in Example 1,following the 3:1 H₂ :CO run as described in Example 1, the feedstreamwas changed to 1:1 H₂ :CO and the hydrocarbon synthesis run was carriedout at a temperature of about 270° C., a total pressure of 394 psia, anda space velocity of about 1737 v/v/hr.

The results for both catalysts, expressed in percent CO conversion vs.time, is given below in Table III.

                  TABLE III                                                       ______________________________________                                        Time         % CO Conversion                                                  (Minutes)    Fe/Ti/Zn/Ce                                                                              Fe/Ti/Zn/K                                            ______________________________________                                        530          21                                                               610          22                                                               685          23                                                               765          23                                                               845          24                                                               930          --         1                                                     1015         --         1                                                     1090         --         1                                                     1170         --         1                                                     1250         --         1                                                     ______________________________________                                    

As is seen, operating with a 1:1 H₂ :CO ratio increases the differentialin activity to about twenty-fold between the two catalysts undersubstantially the same process conditions.

EXAMPLE 3 Catalyst Preparation

The following materials were placed into a blender and mixed for about1/2-hour:

    ______________________________________                                                                  Gram    Relative                                                              Atoms   Gram                                        Component    Wt. (Grams)  Metal   Atoms                                       ______________________________________                                        Fe.sub.2 O.sub.3                                                                           143.0        1.79    1.000                                       Ce.sub.2 (CO.sub.3).sub.3.5H.sub.2 O                                                       16.5         0.06    0.030                                       TiO.sub.2    41.7         0.53    0.300                                       ZnO          10.0         0.12    0.065                                       ______________________________________                                    

Thirty grams of the resulting mixed solid were placed into a 250 ml.flask. Thirty ml. of distilled water was added and the contents werestirred for one hour, after which the contents were heated, producing aslurry. A mild vacuum was applied to remove water from the slurry, andthe resulting solid was dried under 1 mm Hg at 120° C. for 2 hours. Theresulting dried material was pulverized, and the vacuum-drying step wasrepeated for an additional three hours. The solid was pelletized under20,000 psig and sieved to 20/80 mesh material. The resulting solidFe/Ti/Zn/Ce was sintered at 1050° C., in air for 16 hours and wassubsequently used in hydrocarbon synthesis runs described below.

For comparison purposes, the above-described catalyst preparationprocedure was repeated using the following starting materials:

    ______________________________________                                                               Gram    Relative                                                  Weight      Atoms   Gram                                           Component  Grams       Metal   Atoms                                          ______________________________________                                        K.sub.2 CO.sub.3                                                                         4.14        0.06    0.030                                          ZnO        10.0        0.12    0.065                                          TiO.sub.2  41.7        0.53    0.300                                          Fe.sub.2 O.sub.3                                                                         143.0       1.79    1.00                                           ______________________________________                                    

producing a Fe/Ti/Zn/K (empirical formula) solid.

Hydrocarbon Synthesis Run

A sample comprising 8.3 grams of the Fe/Ti/Zn/Ce solid prepared abovewas placed into the reactor apparatus described in Example 1 andpretreated by heating in a 9:1 H₂ :N₂ atmosphere at 500° C., 0.77 MP_(a)A (approximately 115 psia) and 100 v/v catalyst/hr. space velocity for 6hours.

The run was conducted by contacting the catalyst with a 3:1 H₂ :COfeedstream at a space velocity of 870 v/v/hr., a pressure of 2.6 MP_(a)A (approximately 394 psia), and a temperature of 270° C. for 30 hours.

The percent CO conversion as a function of time, and weight percentselectivities of products in terms of carbon numbers, are given below inTables IV and V, respectively.

As is seen in Table IV, the Ce containing catalyst is more active thanthe K containing analog.

                  TABLE IV                                                        ______________________________________                                        On-Stream Time % CO Conversion                                                (Minutes)      Fe/Ti/Zn/Ce                                                                              Fe/Ti/Zn/K                                          ______________________________________                                        660            55         --                                                  720            53         --                                                  770            54         --                                                  860            54         --                                                  940            55         --                                                  1420           --         21                                                  1500           --         22                                                  1580           --         24                                                  1670           --         26                                                  1740           --         27                                                  ______________________________________                                    

As is seen in Table V, the Ce containing catalyst generates lowermolecular weight products than the K containing analog.

                  TABLE V                                                         ______________________________________                                        Product Selectivities                                                                     Wt. %                                                             Carbon No.    Fe/Ti/Zn/Ce                                                                              Fe/Ti/Zn/K                                           ______________________________________                                        C.sub.1       41         20                                                   C.sub.2       31         21                                                   C.sub.3       20         22                                                   C.sub.4       9          17                                                   C.sub.5       7          13                                                   C.sub.6       6           3                                                   C.sub.7       5           1                                                   ______________________________________                                    

EXAMPLE 4

A fifty gram sample of the Fe/Ti/Zn/Ce solid prepared in Example 3,prior to sintering, was placed in a homogenizer and 0.98 g. K₂ CO₃ wasadded to produce a solid containing an approximately 1:1 K/Ce atomicratio and having the following composition:

    ______________________________________                                                                Gram    Relative                                                  Weight      Atoms   Gram                                          Component   Grams       Metal   Atoms                                         ______________________________________                                        Fe.sub.2 O.sub.3                                                                          143.0       1.79    1.0                                           TiO.sub.2   41.7        0.53    0.30                                          ZnO         10.0        0.12    0.065                                         K.sub.2 CO.sub.3                                                                          4.14        0.06    0.030                                         Ce(CO.sub.3).sub.2.5H.sub.2 O                                                             16.5        0.06    0.030                                         ______________________________________                                    

The solid was then treated by the "slurry" method as described inExample 3, and subsequently was sintered and pretreated as described inExample 3.

The pretreated catalyst was then contacted with a 1.0:1.0 H₂ /COfeedstream at a temperature 280° C., a pressure of 2.0 MPaA and a spacevelocity of 870 v/v/hr. The ethylene product was measured by gaschromatographic analysis over the run and the results given in Table VI.

As is seen in Table VI, this catalyst generates a C₂ -C₄ fraction richin ethylene.

                  TABLE VI                                                        ______________________________________                                                      Wt. % Ethylene in C.sub.2 -C.sub.4                              % CO conversion                                                                             Fraction                                                        ______________________________________                                         5            60                                                              15            50                                                              38            28                                                              ______________________________________                                    

EXAMPLE 5

The catalysts prepared in Examples 3 and 4 comprising potassium, cerium,and about a 1.0:1.0 atomic ratio of potassium to cerium were run undersubstantially the same pretreatment and hydrocarbon synthesisconditions.

The catalysts were pretreated at 500° C., with 9:1 H₂ :N₂ flowstream ata space velocity of about 800 v/v/hr. for about 5 to 6 hours.

The catalysts then were each contacted with a 1:1 H₂ :CO feedstream, ata pressure of 2.6 MPaA, a space velocity of 870 v/v/hr., and atemperature of 270° C. for a period of 30-50 hours to achieve steadystate operation. The percent CO conversion values and productdistribution data was collected 5-10 hours after steady state operationwas achieved and was analyzed by gas chromatography versus knownstandards. The results for the three catalysts is listed in Table VII.

                  TABLE VII                                                       ______________________________________                                        Fischer-Tropsch Performance of                                                Fe/Ti/Zn/M, where M = K, Ce, or K/Ce                                          Catalyst M =   K          Ce     K/Ce                                         ______________________________________                                        % CO Conversion                                                                              2.0        17.0   24.0                                         Wt. % Selectivity                                                             CH.sub.4       42         24.5   14.8                                         C.sub.2.sup.=  19         7.5    19.7                                         C.sub.2 °                                                                             6          14.6   9.3                                          C.sub.3.sup.=  23         6.6    12.8                                         C.sub.3 °                                                                             tr         tr     2.9                                          C.sub.4.sup.+  10         46.8   40.5                                         C.sub.2.sup.= /C.sub.2 °                                                              3.2        0.5    2.1                                          ______________________________________                                    

EXAMPLE 6

A series of catalysts with a general composition of Fe/Mn/Zn/M, whereM═K, Ce, or K/Ce, were prepared by the procedure described in Example 2.The promoters, in quantities listed below, were each added to a mixtureof Fe₂ O₃ (70.5 gm), MnO₂ (78.0 gm), and ZnO (5.0 gm).

    ______________________________________                                        M =            K          Ce     K/Ce                                         ______________________________________                                        K.sub.2 CO.sub.3 (gm)                                                                        2.94       0       2.94                                        Ce.sub.2 (CO.sub.3).sub.3.5H.sub.2 O (gm)                                                    0          10.4   10.40                                        ______________________________________                                    

These catalysts were examined under the Fischer-Tropsch conditionslisted in Table VIII. Analysis of the results again shows thesynergistic effect of the two promoters to enhance activity andselectivity for the production of low molecular weight olefins.

                  TABLE VIII                                                      ______________________________________                                        Fischer-Tropsch Performance of                                                Fe/Mn/Zn/M, where M = K, Ce, or K/Ce                                          Catalyst M =   K          Ce     K/Ce                                         ______________________________________                                        % CO Conversion                                                                              18.0       62.5   54.9                                         Wt. % Selectivity                                                             CH.sub.4       10.2       17.5   7.5                                          C.sub.2.sup.=  9.5        3.9    9.6                                          C.sub.2 °                                                                             2.0        7.1    1.1                                          C.sub.3.sup.=  19.7       16.7   14.8                                         C.sub.3 °                                                                             2.1        2.9    1.5                                          C.sub.4.sup.+  56.5       51.9   65.5                                         C.sub.2.sup.= /C.sub.2 °                                                              4.8        0.6    8.7                                          ______________________________________                                         Conditions: 305° C., 2.0 MPa, 1:1 H.sub.2 :CO, 870 v/v/hr         

As is seen, the K/Ce containing catalyst provides high activity, low CH₄selectivity and high C₂ and C₃ olefin selectivity, i.e., greaterproductivity of desired and lower productivity of undesired products,such as methane, relative to the potassium or cerium analogs.

EXAMPLE 7

The potassium-cerium promoted catalyst from Example 3 was subjected topre-reduction with hydrogen at 500° C. for 6.0 hours. The catalyst wasthen subjected to the reaction conditions shown in Table VIII. Theselectivity to C₂.sup.═ -C₄.sup.═ was ≧30% even at high carbon monoxideconversion levels. A slight reduction in C₂.sup.═ -C₄.sup.═ selectivitywas noted in systems which employed high (≧3:1) H₂ :CO feed ratios, asshown in Table IX.

                  TABLE IX                                                        ______________________________________                                        Evaluation of Fe/Ti/Zn/K/Ce at High Conversion Conditions                     ______________________________________                                        Conditions:                                                                   Temp (°C.)                                                                           285° C.                                                                            285° C.                                                                        270° C.                              Pressure (MPa)                                                                              2.6         2.6     2.6                                         H.sub.2 :CO   1:1         1:1     3:1                                         SHSV (v/v/hr) 550         870     550                                         % CO Conversion                                                                             97          85      82                                          Wt. % Selectivity                                                             CH.sub.4      6.0         5.8     8.7                                         C.sub.2.sup.= 11.3        11.4    7.3                                         C.sub.2 °                                                                            7.6         1.9     5.7                                         C.sub.3.sup.= 16.5        16.4    16.0                                        C.sub.3 °                                                                            tr          tr      3.5                                         C.sub.4.sup.= 8.9         12.5    6.8                                         C.sub.4 °                                                                            2.5         6.4     8.9                                         C.sub.5.sup.+ 47.2        55.6    43.1                                        C.sub.2.sup.= /C.sub.4.sup.=                                                                36.7        40.3    30.1                                        ______________________________________                                    

EXAMPLE 8

A comparative test was conducted of two catalysts having thecompositions listed in Table X. The cerium-containing catalyst wasprepared by the procedure listed in Example 1. The cupricoxide-containing catalyst was prepared by the procedure described inU.S. Pat. No. 4,199,523, the disclosure of which is incorporated hereinby reference. Samples comprising 0.3 grams of each catalyst were placedin a Mettler Thermogravimetric Analyzer and were heated under flowinghydrogen gas from 25° to 500° C. at a linear temperature ascending rateof 10° C./min., while continuously monitoring the weight loss.

The cerium-containing catalyst lost about 2% of weight upon heating upto 400° C., while the copper-containing catalyst lost above 10% of itsweight.

This clearly demonstrates that the replacement of CuO with CeO₂ leads tosignificantly different behavior of the mixed oxide matrix underreducing conditions.

                  TABLE X                                                         ______________________________________                                                  Sample No. 1                                                                           Sample No. 2                                                         Wt. %    Wt. %                                                      ______________________________________                                        Fe.sub.2 O.sub.3                                                                          86.0       74.40                                                  ZnO         6.02        5.20                                                  K.sub.2 O   1.70        4.20                                                  CeO.sub.2   6.28       --                                                     CuO         --         16.20                                                  ______________________________________                                    

What is claimed is:
 1. A hydrocarbon synthesis catalyst compositioncomprising sintered combination metal oxides having the followingcomponents in the stated weight percentage of the catalystcomposition:(a) about 5 to about 80 weight percent of a Group VIII metaloxide; (b) about 4 to about 20 weight percent of a Group IIB metaloxide; (c) about 10 to about 40 weight percent of a Group IVB and/orVIIB metal oxide; (d) about 1 to about 5 weight percent of a Group IAmetal oxide; and, (e) about 1 to about 10 weight percent of a LanthanumGroup metal oxide, such that where the catalyst contains a Group VIIImetal, said sintered combination comprises a series of spinels of aGroup VIII metal, a Group IIB metal, and/or a Group IVB metal, and/or aGroup VIIB metal, and a Group IA metal oxide in a Lanthanum Group metaloxide matrix.
 2. The catalyst of claim 1 wherein the Lanthanide groupmetal oxide comprises cerium oxide.
 3. The catalyst of claim 2 whereinthe Group IV metal oxide comprises titanium dioxide and the Group VIIBmetal oxide comprises manganese oxide.
 4. The catalyst of claim 3wherein the Group IIB metal comprises zinc oxide.
 5. The catalyst ofclaim 4 wherein the Group VIII metal oxide comprises iron oxide.
 6. Thecatalyst of claim 5 wherein the Group IA metal oxide is selected fromthe group of oxides consisting of cesium, rubidium, potassium andmixtures thereof.
 7. A hydrocarbon synthesis catalyst compositioncomprising sintered combination metal oxides having the followingcomponents in the stated weight percentage of the catalystcomposition:(a) about 5 to about 80 weight percent Fe oxide; (b) about 4to about 20 weight percent Zn oxide; (c) about 10 to about 40 weightpercent Ti and/or Mn oxide; (d) about 1 to about 5 weight percent K, Rb,and/or Cs oxide; and (e) about 1 to about 10 weight percent Ce oxide,such that where the catalyst contains Fe, said sintered combinationcomprises a series of Fe, Zn, and/or Ti and/or Mn spinels and oxides ofK, Rb and/or Cs, dispersed in a Ce oxide matrix.
 8. The catalystcomposition of claim 7 exhibiting an X-ray diffraction pattern of aniron-containing spinel, or mixture thereof and cerium oxide.
 9. Thecatalyst composition of claim 8 wherein said spinel is magnetite,Fe_(3-x) Mn_(x) O₄, Fe_(3-x) Zn_(x) O₄, Fe_(3-x) Ti_(x) O₄ or a mixturethereof wherein x ranges between about 0.15 and about 2.4.
 10. Thecatalyst composition of claim 7 wherein said cerium oxide is present asa homogeneously distributed component.
 11. The catalyst composition ofclaim 7 wherein component (c) is titanium dioxide.
 12. The catalystcomposition of claim 7 wherein component (d) is K oxide.
 13. Thecatalyst composition of claim 7 wherein component (d) is present in lessthan 2 weight percent of the catalyst composition.
 14. The catalystcomposition of claim 7 wherein component (e) is present as from about 2to about 5 weight percent of the catalyst composition.
 15. The catalystcomposition of claim 7 supported on an inert support.
 16. The catalystcomposition of claim 15 wherein the inert support is selected from thegroup consisting of alumina, silica and magnesia.
 17. The catalystcomposition of claim 7 wherein the metal atoms are present in thefollowing ratios:(a) about 0.8-1.2 Fe (b) about 0.05-0.08 Zn (c) about0.25-0.35 Ti and/or Mn (d) about 0.010-0.15 Ce (e) about 0.010-0.15 K.18. The catalyst composition of claim 17 wherein the metal atoms arepresent in about the following ratios:(a) 1.0 Fe (b) 0.065 Zn (c) 0.30Ti and/or Mn (d) 0.030 Ce (e) 0.030 K.
 19. A process for preparing thecatalyst composition of claim 7 comprising the steps of:(a) slurrying anaqueous suspension of oxides and/or carbonates of: iron; zinc; titaniumand/or manganese; the carbonates of potassium, rubidium, and/or cesium;and cerium carbonate; (b) heating the aqueous slurry to at least about90° C.; and, (c) sintering the resulting solid in an oxygen-containingatmosphere, at a temperature in the range of about 400° C. to about1200° C. until the X-ray diffraction pattern of the solid issubstantially that of at least one iron-containing spinel, in an oxidematrix comprising CeO₂.
 20. The process of claim 19 wherein theresulting solid is sintered at a temperature of about 1,000° C. to about1,200° C. for a period of time ranging between about 16 to 24 hours.